Modern wireless telecommunications systems are evolving to provide high speed packet data services for users of mobile equipment. One example is an ability to provide internet access to a user of mobile equipment. A wireless system that is rapidly evolving in this direction is a Time Division, Multiple Access (TDMA) system known as the Global System for Mobile Communication (GSM), in particular enhanced versions of GSM known as GSM+, GPRS (General Packet Radio Services) and EGPRS (Enhanced General Packet Radio Services).
The GPRS Release '97 was the first standard to provide (limited) packet data services. However, this standard did not provide a capability for the user to control the bit rate(s) and delays for a packet data connection. In the developing Universal Mobile Telecommunication System (UMTS) packet domain permits several packet data connections to be simultaneously maintained, with different qualities of service. Although there have, at present, been two subsequent GPRS releases since the Release '97, the quality of service concept has remained the same.
The Enhanced GPRS (EGPRS) phase 2, which is expected to be the next GPRS release (Release '00), provides a new radio access network to the UMTS core network, and is to adopt the same quality of service attributes as used in the existing UMTS.
A problem thus has arisen, as to how the basic GPRS quality of service provisions can be enhanced to meet the same flexibility requirements that exist in UMTS.
In the UMTS system the data connection between a core network and a mobile station is identified using a Network Service Access Point Identifier (NSAPI), that identifies as well a radio access bearer. In the previous releases of GPRS (pre-Release '00), a connection is identified by NSAPI and a Logical Link Control (LLC) protocol SAPI. However, in UMTS, and thus in GPRS Release '00, the LLC protocol is no longer used.
More specifically, in the UMTS a data connection between a mobile station (MS), such as a cellular telephone, and the third generation (3G) Serving GPRS Support Node (SGSN), or 3G-SGSN, is identified using the Network Service Access Point Identifier (NSAPI) with which the requested quality of service parameters are associated. The data connection is realized by a radio access bearer established by the 3G-SGSN to the radio access network. The radio access bearer identity is the same as the NSAPI. In the radio interface the radio access bearer is realized by one or several radio bearers, each having their own identities. During the radio bearer set-up phase the NSAPI is associated with radio bearers and the radio bearers are associated with a channel. As such, in the UMTS radio access network the channel number/identifier unambiguously identifies the data connection and its quality of service parameters and, hence, there is no need to carry either the NSAPI or radio bearer identity in protocol headers.
However, in GPRS Release '00 there is no provision to associate a data connection to a (physical) channel. As such, one problem that arises is how to identify a data connection in the radio interface.
A second issue relates to improving the flexibility of the GPRS Radio Link Control/Media Access Control (RLC/MAC) layer. An important distinction between the basic GPRS and the UMTS Radio Access Network (URAN) is that the GPRS MAC multiplexes Logical Link (LL) Protocol Data Units (PDUs), while UMTS multiplexes transport (Radio Link Control or RLC) blocks. In general, GPRS multiplexing is inflexible, and is not suitable for connections having different quality of service requirements. For example, whatever the size of the LL PDU from SAPI 5 in FIG. 2 (the maximum length is 1520 octets), it must be entirely sent before the layer 3 message from SAPI 1 can be sent. If the RLC mode used by SAPI 5 is different than the one used for signalling, then the current Temporary Block Flow (TBF) must be released, and a new TBF established before the layer 3 message can be sent. Before sending a new LL PDU, a Packet Resource Request message must be sent to the network to indicate the characteristics (radio priority, peak throughput class, RLC mode) of the new LL PDU.
In EGPRS the same access types as in GPRS are supported to establish the Temporary Block Flow (TBF) in the uplink direction (i.e., from the mobile equipment to the network).
To accomplish this, a control message used by a GPRS mobile equipment to request a packet channel (Packet Channel Request, 11 bits) is re-used for EGPRS.
To summarize, in GPRS '97 a data connection is identified by the NSAPI carried in a SNDCP (Subnetwork Dependent Convergence Protocol) header and by a LLC SAPI carried in a LLC protocol header. However, in GPRS Release '00 the SNDCP is replaced with Packet Data Convergence Protocol (PDCP) that does not have NSAPI in a protocol header, and the LLC protocol is removed. As such, the GPRS Release '97 type of identification cannot be directly used, while in UMTS the NSAPI is not required to be carried in the protocol header, as the NSAPI/radio bearer/channel mapping is done unambiguously.
With regard to multiplexing in UMTS, there are two levels of data multiplexing. First, the MAC multiplexes logical channels onto the transport channel. The basic multiplexing unit is a PDCP PDU, hence MAC multiplexing has the same properties as the LLC PDU multiplexing in a GPRS RLC. For example, and referring to FIG. 3, if radio bearer x has a higher priority than radio bearer y, and if they are multiplexed onto the same transport channel (Dedicated Transport Channel or DCH) 2, then a Packet Data Convergence Protocol (PDCP) Protocol Data Unit (PDU) from the radio bearer x cannot be sent before a previous PDCP PDU from the radio bearer y has been sent. Transport channels are connected to a layer 1 coding and multiplexing unit that processes and multiplexes several dedicated transport channels into a coded composite transport channel (CCTrCH). Bits from the CCTrCH can be mapped on the same physical channel, as shown in FIG. 3. The only restriction is that transport channels should have the same Carrier to Interference (C/I) requirement, therefore both speech and data cannot be mapped onto the same physical channel. Each transport channel has its own transport format set. On the physical channel all combinations of transport formats cannot be supported, but only a subset that is defined in the transport format combination set. When mapping data onto a physical channel, MAC chooses between the different transport format combinations given in the transport format combination set. This selection is performed rapidly and utilizes a flexible variable bit rate scheme for the physical layer without requiring additional signalling. If, in FIG. 3, radio bearers x and y are mapped on the different transport channels DCH2 and DCH3, then RLC PDUs from DCH2 can be sent at the same time, or before, RLC PDUs from DCH3, depending on the transport format combination that the MAC transfers to layer 1. However, the total bit rate of the different transport channels cannot exceed at any time the maximum bit rate set of the CCTrCH.
In summary, with the known techniques a data connection is implicitly associated with a Radio Link Control (RLC) Temporary Block Flow (TBF).
To overcome these problems, it has been previously proposed to allow more than one Temporary Block Flow (TBF) to simultaneously exist. However, for several reasons this approach is not optimum.